Carburetor for internal combustion engines

ABSTRACT

A twin carburetor of the variable-area choke type for use in multi-cylinder engine of a motor vehicle which twin carburetor includes a balance tube interconnecting a front side mixture passage and a rear side mixture passage at a point downstream of each throttle valve for balancing the pressures therein to equalize the amounts of air-fuel mixtures to be supplied to individual cylinders of the engine and an additional balance tube interconnecting the front side mixture passage and the rear side mixture passage at a point downstream of each choke for balancing the suctions or depressions acting on each air valve to provide the same effective cross-sectional area at each fuel jet for thereby producing air-fuel mixtures having equal air-fuel ratios in each mixture passage.

[ .ian.8,1974

[ CARBURETOR FOR INTERNAL COMBUSTION ENGINES [75] Inventors: Takakazu Sato; Taknya Mas-ago,

both of Yokohama, Japan [73] Assignee: Nissan Motor Company, Limited,

Yokohama City, Japan [22] Filed: Oct. 11, 1972 [21] Appl. No.: 296,530

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS 935,882 9/1963 Great Britain 123/59 PC Primary ExaminerTim R. Miles Attorney-John Lczdey et a1.

[ 5 7 ABSTRACT A twin carburetor of the variable-area choke type for use in multi-cylinder engine of a motor vehicle which twin carburetor includes a balance tube interconnecting a front side mixture passage and a rear side mixture passage at a point downstream of each throttle valve for balancing the pressures therein to equalize the amounts of air-fuel mixtures to be supplied to individual cylinders of the engine and an additional balance tube interconnecting the front side mixture passage and the rear side mixture passage at a point downstream of each choke for balancing the suctions or depressions acting on each air valve to provide the same effective cross-sectional area at each fuel jet for thereby producing air-fuel mixtures having equal airfuel ratios in each mixture passage.

1 Claim, 1 Drawing Figure CAlRlBURETOR FOR INTERNAL COMBUSTION ENGINES This invention relates to carburetors of the variablearea choke type for internal combustion engines, particularly for multi-cylinder engines used in motor vehicles, and relates principally to twin carburetors of the type which are adapted to improve the engine performance efficiency throughout various operating conditions of the engines.

A well known carburetor of this type, known as the S.U. twin carburetor, usually includes an air valve provided upstream of a throttle valve and movable in dependence on the suction or depression prevailing at the choke of the carburetor, the air valve carrying thereon a tapered metering needle adapted to vary the open effective cross-sectional area of a fuel jet thereby to vary the air-fuel ratio of an air-fuel mixture to be supplied to groups of individual cylinders of an internal combustion engine. ln the carburetor of this kind, as the engine speed or the engine load increases, then the effective choke area and accordingly the effective cross-sectional area of the fuel jet are enlarged since the air valve lift is proportional to the volume of air passing through the throttle valve.

Conventional twin carburetors of the type abovespecified usually employ a front side mixture passage having therein a front side throttle valve and a rear side mixture passage having therein a rear side throttle valve. In the carburetors of this kind the arrangement is such that the front side throttle valve and the rear side throttle valve are opened simultaneously through the use ofa suitable common throttle actuating mechanism. ln the carburetors of this kind, it is a common practice to provide a throttle actuating mechanism for opening and closing both throttle valves to the same ratio with a view of supplying the groups of individual engine cylinders with an equal amount and equal airfuel ratio of the air-fuel mixture. If, in this instance, there exists a differential opening between these throttle valves under light-load conditions, the groups of individual cylinders of the engine can not receive equal charges of air and fuel throughout varying operating conditions of the engine. This is reflected by reduction in the maximum possible power output and irregular operation of the engine. In order to solve this problem, it has heretofore been proposed to have the twin carburetors of the type above-described equipped with a balance tube connecting the front side and rear side mixture passages at a point downstream of each of the throttle valves with a view of balancing the pressures and thus ensuring a more equal mixture distribution to the individual cylinders. A difficulty is encountered in this prior art method is that, if there is a pressure difference between the front side mixture passage and the rear side mixture passage at a point downstream of each choke due to differencial opening between the two throttle valves, different extents of valve lifts are caused in the air valves of the front side and rear side mixture passages and, therefore, the fuel jets of the front side and rear side mixture passages are opened to different degrees. This results in uneven charges of fuel from each fuel jet to provide air-fuel mixtures of unequal air-fuel ratios which invites irregular operation of the engine.

It is, therefore, an object of the present invention to provide a new and improved carburetor of the variablearea choke type for use in an internal combustion engine of a motor vehicle whereby a maximum engine performance efficiency will be obtained throughout varying operating conditions of the engine.

Another object of the present invention is to provide a new and improved twin carburetor of the type abovespecified for use in a multi-cylinder engine of a motor vehicle.

Still another object of the present invention is to provide a twin carburetor of the type above-specified which is capable of increasing engine performence efficiency throughout various operating conditions of the engine.

A further object of the present invention is to provide a twin carburetor of the type above-specified which is adapted to improve the charging of the groups of individual cylinders of the engine and therefore engine performance efficiency.

A further object of the present invention is to provide a twin carburetor of the type above-specified which is arranged to supply the groups of individual cylinders of the engine with air-fuel mixtures of equalized air-fuel ratios.

A still further object of the present invention is to provide a twin carburetor of the type above-specified which is arranged to equalize the air-fuel ratios of airfuel mixtures to be delivered to individual cylinders of a multi-cylinder engine and to give equal mixture distribution to the groups of individual cylinders for thereby improving engine performance efficiency.

According to the present invention, a twin carburetor of the variable-area choke type is provided which is specifically adapted for use in a multi-cylinder engine ofa motor vehicle. This carburetor includes a front side mixture passage having therein a front side throttle valve and a rear side mixture passage having therein a rear side throttle valve, the arrangement being such that the front side and rear side throttle valves are simultaneously opened. In a preferred embodiment, the twin carburetor is provided with a first balance tube connecting the front side mixture passage and the rear side mixture passage at a point downstream of respective throttle valves and a second balance tube connecting the front side mixture passage and the rearside mixture passage at a point between the choke and the throttle valve. The first balance tube serves to balance the pressures in the front side and rear side mixture passages downstream of the respective throttle valves for thereby equalizing the quantities of air-fuel mixtures to be supplied through respective mixture passages to the groups of individual cylinders. The second balance tube serves to balance the pressures in the front side and rear side mixture passages downstream of the respective chokes for equalizing the extents of lifts of respective air valves so that an equal cross sectional area is obtained at each fuel jet of each mixture passage for thereby producing air-fuel mixtures of present invention is specifically suited for use in a multi-cylinder engine of a motor vehicle. As shown, the twin carburetor includes as customary a front side and a rear side 10'. The front side 10 is composed of a front side mixture passage 12 which communicates with intake manifolds 14 of the engine which intake manifolds lead to a series of groups of individual cylinders (not shown), a front side throttle valve 16 mounted in the front side mixture passage 12 for controlling the quantity of air-fuel mixture to be supplied to the individual cylinders through the intake manifolds 14, and a choke 18 including an air valve or flow regulating means 20 and a constriction or bridge 22. The front side 10 is also composed of a fuel jet 24 through which fuel is drawn into the choke 18. The air valve 20 comprises a casing 26 and a movable suction piston 28 of known construction. A metering needle is carried on the bottom wall of the suction piston 28 and extends into the fuel jet 24 for metering the amount of fuel to be drawn into the choke 18. The metering needle 30 is tapered toward its tip for continuously changing the open effective cross-sectional area of the fuel jet 24 for thereby varying the amounts of fuel to be drawn into the choke 18 as the suction piston 28 and accordingly the metering needle 30 move upwardly and downwardly in response to the fluctuations in the depression in the front side mixture passage 12 upstream of the front side throttle valve 16 to thereby vary the effective cross-sectional area at the choke 18 into which the liquid fuel is drawn from the fuel jet 24. When the front side throttle valve 16 is near a closed position, the suction piston 28 will move downwardly of the drawing to close off the choke 18 and little air will flow across the bridge 22. When, however, the throttle valve 16 assumes a wide open or full power position, the pressure difference across the choke 18 will cause the suction piston to move upwardly of the drawing the maximum amount, thereby allowing the greatest massive air flow to take place and the fuel jet will be restricted by the metering needle to the least degree. Similarly, the rear side 10' is composed of a rear side mixture passage 12 communicating with intake manifolds 14' leading to another series of individual cylinders (not shown), a rear side throttle valve 16' mounted in the rear side mixture passage 12' for controlling the quantity of airfuel mixture to be supplied to the individual cylinders through the intake manifolds 14', and a choke 18' including an air valve or flow regulating means 20 and a constriction or bridge 22'. The rear side 10 is also composed ofa fuel jet 24 through which fuel is drawn into the choke 18' The air valve 20 comprises a casing 26' and a movable piston 28' of known construction, the suction piston 28 carrying at its bottom wall a metering needle 30' which extends through the fuel jet 24' for varying the effective cross-sectional area of the fuel jet 24.

The front side throttle valve 16 and the rear side throttle valve 16 are associated with each other by means of a suitable common throttle actuating mechanism so that these throttle valves are opened simultaneously to the same opening degree for supplying the groups of individual cylinders with air-fuel mixtures of equal quantities and equal air-fuel ratios, respectively. If, however, there exists a difference in opening degrees between the two throttle valves as seen in the drawing, that is, if the the opening degree of the, e.g., front side throttle valve 16 is larger than that of the rear side throttle valve 16', then the front side throttle valve 16 permits the air-fuel mixture to flow into the intake manifolds 14 at an amount which is larger than that delivered through the rear side mixture passage 12'. This causes irregular operation of the engine and therefore reduction in power output.

To eliminate this drawback, a balance tube 32 is provided in the twin carburetor. As shown in the drawing, the balance tube 32 is connected between the front side mixture passage 12 and the rear side mixture passage 12' at a point downstream of each throttle valve. This balance tube 32 serves to balance the pressures P, and P prevailing in the front side mixture passage 12 and the rear side mixture passage 12 downstream of the front side throttle valve 16 and the rear side throttle valve 16', respectively, so that same amounts of air-fuel mixtures are drawn into the intake manifolds l4 and 14, respectively. With this arrangement, if the pressure P (prevailing downstream of throttle valve 16') is smaller than the pressure P, (prevailing downstream of throttle valve 16), then the air-fuel mixture passing through the front side throttle valve 16 in passageway 12 is partially admitted into the rear side mixture passage 12 downstream of the rear side throttle valve 16 as shown by un-numbered arrows and, therefore, the air-fuel mixtures are equally distributed to the groups of individual engine cylinders thereby improving engine performance efficiency.

In accordance with an important feature of the present invention, there is provided in the twin carburetor an additional balance tube 34 with a view of equalizing the air-fuel ratios of the air-fuel mixtures to be delivered to the groups of individual cylinders. As shown, the balance tube 34 is interconnected between the front side mixture passage 12 and the rear side mixture passage 12' at a point downstream of each choke l8 and 18'. This balance tube 34 serves to balance the suctions or depressions S, and S prevailing in the front side mixture passage 12 and the rear side mixture passage 12' downstream of the chokes 18 and 18', respectively, so that the valve lifts of the air valves 20 and 20 are equalized to cause the respective metering needles 30 and 30 to move to the same extent for thereby providing equal cross-sectional area at the fuel jets 24 and 24, respectively.

If, in operation, the front side throttle valve 16 is open to a larger degree than the rear side throttle valve 16', then the depression S, prevailing downstream of the choke 18 is larger than the depression S prevailing in the rear side mixture passage 12'. In this instance, the depression S,, is partially transmitted through the balance tube 34 into the rear side mixture passage 12' downstream of the choke 18' as shown by unnumbered arrows until the latter reaches the level of the depression S,. Accordingly, the (extents of) valve lifts (h, and k are equalized so that the metering needles 30 and 30' provide equal cross-sectional areas at the fuel jets 24 and 24' thereby producing air-fuel mixtures having an equal air-fuel ratio at the chokes l8 and 18', respectively.

It will now be appreciated from the foregoing description that the twin carburetor of the present invention advantageously incorporates an additional balance tube interconnecting the front side mixture passage and the rear side mixture passage at a point downstream of each choke whereby the depressions acting on the air valves are equalized to provide the same extents of valve lifts for providing the same effective crosssectional areas at the fuel jets for thereby equalizing the air-fuel ratios of air-fuel mixtures to be supplied to the individual engine cylinders.

While only one preferred embodiment of the present invention has been illustrated and described in detail, it is to be expressly understood that the present invention is not limited thereto. Various modifications and changes may be made without departing from the scope of the present invention as the same now be understood by those skilled in the art.

What is claimed is:

l. A twin carburetor for an internal combustion engine of a multi-cylinder type comprising at least two mixture passages adapted to supply air-fuel mixtures to groups of individual cylinders of said engine, at least two throttle valves disposed in said mixture passages respectively for controlling the amounts of the air-fuel mixtures to be supplied to said groups ofindividual cylinders, at least two chokes provided upstream of said throttle valves, respectively, each of said chokes including a movable air valve and a constriction, at least two fuel jets each opening into each of said chokes for supplying fuel thereinto, and a balance tube interconnecting said two mixture passages at a point downstream of said throttle valves for balancing the pressures in said mixture passages downstream of said throttle valves for thereby equalizing the amounts of the air-fuel mixtures to be supplied to said groups of individual cylinders, and an additional balance tube interconnecting said two mixture passages at a point downstream of said chokes for balancing the depressions prevailing therein and acting on said air valves for thereby equalizing the air-fuel ratios of the air fuel mixtures to be supplied to said individual groups of cylinders. 

1. A twin carburetor for an internal combustion engine of a multi-cylinder type comprising at least two mixture passages adapted to supply air-fuel mixtures to groups of individual cylinders of said engine, at least two throttle valves disposed in said mixture passages respectively for controlling the amounts of the air-fuel mixtures to be supplied to said groups of individual cylinders, at least two chokes provided upstream of said throttle valves, respectively, each of said chokes including a movable air valve and a constriction, at least two fuel jets each opening into each of said chokes for supplying fuel thereinto, and a balance tube interconnecting said two mixture passages at a point downstream of said throttle valves for balancing the pressures in said mixture passages downstream of said throttle valves for thereby equalizing the amounts of the air-fuel mixtures to be supplied to said groups of individual cylinders, and an additional balance tube interconnecting said two mixture passages at a point downstream of said chokes for balancing the depressions prevailing therein and acting on said air valves for thereby equalizing the air-fuel ratios of the air fuel mixtures to be supplied to said individual groups of cylinders. 